reporter: the haunting similarities between ted's dark letters and a manifesto the unabomber sent to "the washington post" and "new york times" caught the attention of david's wife. >> it kind of added up. he was a woodworker, he had connections to chicago and san francisco. >> linda urged me to sit down and read the manifesto and i'm actually reading the first page, all set to turn to her and say, look, you've been really silly. i'm sure this is not ted's writing. and finding myself with a lump in my chest. >> reporter: for david, it was a horrible realization. >> if you looked past the ideas of the manifesto, you see a person as troubled as my brother. >> reporter: he now had to decide what to do. >> if we do nothing and ted is the unabomber, we may wake up some morning and realize he struck again. an innocent person died because we had failed to act, we would have blood on our hands. >> reporter: it took linda two months but finally convinced david to contact the fbi. >> there was no turning back, but i can't tell you how painful it was to put my finger down and say yes, he lives here, realizing